This invention relates to a stabilization system for improving the melt viscosity of polypropylene (xe2x80x9cPPxe2x80x9d) resin during fiber processing. Specifically, this invention relates to the use of liquid phosphite during fiber processing to provide more uniform control of degradation.
In conventional fiber production processes, polypropylene (PP) fibers are produced by first feeding PP powder or pellets to an extruder which melts the resin and blends it with pigments and other additives. The molten resin is forced through a many-holed die (xe2x80x9cspinneretxe2x80x9d) as continuous strands are air-quenched and then drawn to the final fiber diameter either by mechanical draw or by forced air. The fiber production process induces significant degradation of the PP resin. The extrusion is typically conducted at high temperature to minimize die pressure and maximize throughput rate. The thermal degradation is exacerbated by the shear of mixing and more so by the high shear associated with forcing molten resin through the small orifices of the spinneret. Additional degradation takes place as the resin is quenched from high temperature in an air current.
A key to successful fiber production is maintaining a consistent melt viscosity upstream of the spinneret throughout the production campaign. Variations in melt viscosity may cause process upsets ranging from spinneret over-pressuring to filament breaks. These upsets represent lost production time and often unacceptable cost for the fiber producer. Variations in melt viscosity can also lead to the use of excessive stabilizer concentrations, which result in high costs and poor fiber quality.
Conventional PP resin fiber production methods control melt viscosity upstream of the spinneret by dry-blending granular or powder melt processing stabilizers with PP resin powder prior to extrusion. It is known to dry-blend PP powder with tris(2,4-di-tert-butylphenyl)phosphite. Tris(2,4-di-tert-butylphenyl)phosphite is a processing stabilizer commercially available from Ciba Specialty Chemicals under the tradename Irgafos 168. The extrusion is relied upon to provide thorough mixing of the stabilizers and PP resin before significant degradation can take place. However, the extrusion portion of a conventional fiber process may not provide adequate mixing to ensure uniform distribution of stabilizers throughout the polymer. In addition, due to the high extrusion temperatures used for fiber production, significant polymer degradation can occur before the stabilization additives are well mixed with the PP resin. The resulting non-uniform stabilization and non-uniform degradation may lead to poor melt viscosity control of the PP resin during fiber processing. Therefore, there exists a need for a PP resin system that degrades to a consistent beam melt flow during the extrusion process.
The present invention provides for a stabilization system to improve the melt viscosity control of PP resin during fiber processing. The system consists of a phenolic anti-oxidant and a liquid phosphite dissolved or dispersed in mineral oil or another liquid carrier and applied to PP powder prior to extrusion and/or fiber processing. The present stabilization system is designed to improve the consistency of resin melt viscosity during fiber processing by providing more uniform control of degradation than conventional additives.
The present invention involves a stabilization system for improving the melt viscosity of polypropylene during fiber processing consisting essentially of a phenolic anti-oxidant, a liquid phosphite and a liquid carrier.
Additionally, the present invention involves stabilizer mixture suitable for improving the melt viscosity of polypropylene which mixture consists essentially of approximately 50-100 ppm of a phenolic anti-oxidant, approximately 150-500 ppm of a liquid phosphite and a liquid carrier.
The present invention involves a stabilization system suitable for improving the melt visocisity of polypropylene homopolymer consisting essentially of 50-100 ppm of octadecyl 3,5-di-tert-butyl-4-hydroxyhydrocinnamate phosphite, 150-500 ppm of trisnonylphenol phosphite and mineral oil.
The present invention provides the advantages improving the melt viscosity of polypropylene resin during fiber processing. Those, and other advantages and benefits will become apparent from the Detailed Description of the Invention.